1. Field of the Invention
The present invention relates to wireless networking systems, and more particularly to a coexistive solution for frequency-overlapping wireless communication protocols.
2. Description of the Related Art
Wireless communication and networking protocols are increasingly used to provide connectivity for diverse classes of electronic devices. These wireless protocols permit electronic devices such as computers, personal digital assistants (PDA), and mobile phones to transmit and receive information without the requirement of physically interconnecting the electronic devices to one another or to communications mediums via wire or cable connections. Wireless connectivity in this manner increases portability and flexibility in electronic devices and has become an important method by which data and information is distributed.
Numerous standards have been proposed for use in transmitting and receiving information in wireless local area networks. Two emerging protocols which have received widespread acceptance include Bluetooth (BT) and IEEE 802.11 (WLAN) wireless protocols. These protocols share a common frequency spectrum in the 2.4-GHz Industrial, Scientific, and Medical (ISM) band and are used to exchange information between electronic devices which support the appropriate protocol. Both protocols offer high speed data exchange rates and may be integrated into devices for connecting to land-based or wired communications networks such as the Internet. In general, wireless protocols, such as BT and WLAN, transmit data by superimposing the desired information on a carrier radio wave. Data is recovered through the use of a receiver which specifically tunes to the transmission frequency of the carrier signal to receive the signal and decode the information contained therein.
The Bluetooth protocol is designed primarily for short-range wireless communication between electronic devices in small localized networks (piconets). The network topology in the Bluetooth piconet comprises up to eight active devices, with a maximum of three synchronous-connection-oriented (SCO) links. These SCO links further support real-time communications such as those required for voice or telephony applications. The Bluetooth protocol additionally supports asynchronous connection links (ACL) which are typically used to exchange data and information in non-time critical applications.
Within the piconet topology, only one Bluetooth device may typically transmit at a time. Transmissions are managed using a master/slave relationship wherein one Bluetooth device is designated as a master device and controls other slave device transmissions within the piconet. The master device coordinates transmissions within the piconet by continually polling the slave devices to determine which slave devices require a clear channel to transmit data. Slave devices receive “permission” from the master device before transmitting information and only transmit information when “asked” to do so by the master device. Controlling slave transmission traffic in this manner permits the master device to schedule and manage information exchange within the piconet and prevents data collisions and corruption due to overlapping data transmissions from multiple devices.
The aforementioned SCO link is a symmetric point-to-point link between the master device and a single slave device in the piconet. The SCO link is maintained by the master device using reserved slots or frequencies at regular intervals and typically may not be retransmitted. Therefore, interference or data corruption in SCO transmissions may not be recovered from by retransmission of data packets as is commonly used in other transmission protocols. A problem is encountered when competing or overlapping protocols, such as Bluetooth SCO transmissions, interfere with one another and result in the lack of ability to reconstruct or retransmit the data transmission after corruption or drop-off. In SCO voice transmissions, data corruption of this type may degrade the data exchange to a point where voice communication is no longer practical. As a result, a need exists for a mechanism to insure that non-retransmitable protocols which operate in a frequency-overlapping environment may be afforded a priority to insure unconflicted transmission.
In the aforementioned ACL link, a point-to-multipoint link exists between the master device and the slave devices of the piconet. Using this link type the master device may establish ACL links on a per-slot basis in those slots not reserved for SCO links to permit communication with slave devices. This link type typically supports packet retransmission and although not subject to the dramatic drop-off of transmission quality of SCO links, may still suffer undesirable performance degradation when transmitted in a conflicting manner with another frequency-overlapping protocol.
Bluetooth device communication can be further characterized by the use of a frequency-hopping spread spectrum (FHSS) technique wherein data is transmitted in discrete packets along different frequencies within the 2.4-GHz ISM band. The Bluetooth protocol specifies that frequency hops be made at the rate of approximately 1600 hops/sec such that data exchange takes place with the data spread throughout the ISM band. This type of spread spectrum (SS) technique utilizes a relatively high energy transmission along a narrow band for a limited time.
Alternatively, the WLAN wireless protocols may be used to connect electronic devices in a peer-to-peer network wherein there are no strict servers or hierarchy among communicating devices. In this network topology, each electronic device within the wireless network functions as its own server and determines when to send and receive information without a dedicated administrative server or master device. Devices in the WLAN wireless network contend for access to the available radio frequencies and bandwidth using a sensing and collision avoidance protocol to improve the rate of data and information transmission.
WLAN device communication can be further characterized by the use of a direct-sequence spread spectrum (DSSS) wherein data is transmitted along a wide bandwidth with relatively low energy. Typically, DSSS divides the available ISM band into eleven to fourteen sub-channels for different countries over the world. Each DSSS network will use a band of several channels centered at one of these standard sub-channels. In a multiple access-area network, overlapping and/or adjacent areas using different channels can operate simultaneously without interference if the distance between the center frequency is at least 30 MHz. WLAN protocols occupy these fixed channels of the ISM band, (passbands), to transmit and receive information between compatible devices.
While the aforementioned wireless protocols function well in environments where only one wireless protocol in the ISM band is in operation, a problem arises in local area networks wherein both Bluetooth and WLAN devices coexist. The shared frequency range of the two protocols inevitably results in transmission interference and data corruption as the two protocols operate with transmission frequencies that overlap at various times during routine transmission of information. The resulting frequency overlap degrades the network performance and transmission rates in both families of devices due to a lack of ability of wireless devices which use differing protocols to coordinate their data transmissions. This problem is exacerbated as the number of wireless devices within the network increases and is further affected by the proximity in which the wireless devices are placed with respect to one another. Thus, in order to prevent undue network performance degradation there is a need in the prior art for, a compensation scheme to facilitate the coexistence of shared frequency network topologies such as those used by BT and WLAN protocols.
The widespread acceptance of both the Bluetooth and WLAN wireless protocols has further lead to the manufacture of a large number of electronic devices which typically incorporate only a single wireless technology or protocol for network communication. This creates an additional problem as there are many existing wireless networks which necessarily dictate the type of wireless protocol which can be used within the network or in the vicinity of those devices in the network. Wireless devices which do not comply with the protocol of the existing wireless network may be incompatible with the network and may be precluded from use. Thus, a user may be denied access to wireless devices which cannot be integrated into the existing wireless network infrastructure because of conflicting wireless standards. In the absence of a unifying device which permits the use of more than one wireless standard in the same service area, existing wireless devices in the network may be required to be replaced with updated devices which are capable of communicating using multiple wireless standards to prevent timing and data collisions. Clearly, device replacement in this manner is undesirable as it may be prohibitively expensive and preclude the use of wireless devices which operate with differing frequency-overlapping protocols.
Based on the foregoing, a need exists for a system to facilitate the coexistence of wireless devices which operate with different frequency-overlapping protocols such as the Bluetooth and WLAN wireless protocols. A desirable feature of such a system is to permit the use of existing wireless devices without substantial modification. Furthermore, this system should manage cross-protocol trafficking to reduce collisions and interference between the wireless protocols using mixed topologies so as to permit wireless devices with differing protocols to function within the same transmission area.